<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    .contain{
      width: 100%;
      height: 400px;

    }
    .left{
      width: 200px;
      height: 100%;
      float: left;
      background-color: #4CAF50;
    }
    .right{
      width: 200px;
      height: 100%;
      float: right;
      background-color: yellow;
    }
    .main{
      margin-left: 200px;
      margin-right: 200px;
      height: 100%;
      background-color: red;
    }

  </style>


</head>
<body>
<div class="contain">
  <div class="left"></div>
  <div class="right"></div>
  <div class="main">12121212</div>
</div>



</body>
</html>